Electron microscopic histochemistry of lysosomes in neurosecretory nerve endings and pituicytes of rat posterior pituitary

Summary Electron microscopic localization of acid phosphatase (AcPase) was carried out on posterior pituitary glands from rats. An estimated 5% of the neurosecretory nerve terminals contained structures which showed reaction product. Most of the lysosomes were small dense bodies, often with a membranous substructure. Other lysosomes were larger in size or were found within vacuoles. AcPase was also localized to lysosomes and the Golgi apparatus of pituicytes. Evidence is presented which would associate the large lipid droplets characteristic of pituicytes with AcPase-positive dense bodies. The present study indicates that hydrolytic activity by lysosomes occurs within the terminals of neurosecretory cells, and adds further support to the concept that this process represents a normal phenomenon of cells and their extensions in general.Supported by the Medical Research Council of Canada.Medical Research Associate of the Medical Research Council of Canada.     

Comparative studies on human skin fibroblasts: Life span and lipid metabolism in medium containing fetal bovine or human serum

Summary Three strains of human skin fibroblasts were cultivated in nutrient medium supplemented either with human serum or fetal bovine serum, and growth and lipid synthesis were compared. Rates of cellular growth were similar in both kinds of medium, but the replicative life spans of all three strains were curtailed significantly in human-serum medium. Incorporation of label into the major classes of neutral lipids from [¹⁴C]acetate and³H₂O was increased also in human-serum medium. Since human serum contained higher concentrations of cholesterol known to reduce endogenous cholesterol synthesis, these results were unexpected. Nonlipid factors in human serum may account for the shortened cellular life spans and increased lipogenesis and perhaps for the potential to develop atherosclerosis. Supported by grants from the Ontario Heart Foundation and Medical Research Council of Canada during the tenure of a Senior Research Fellowship from the Ontario Heart Foundation (J.T.C.) and a Scholarship from the Medical Research Council of Canada (S.G.).     

Purification and properties of two distinct groups of ADH isozymes from Chinese hamster liver

Two major classes of alcohol dehydrogenase isozymes have been purified from Chinese hamster liver. The two isozyme classes have the same subunit molecular weights but different electrophoretic mobilities. They have a similar range of substrates but different KROM values and sensitivities to the inhibitor pyrazole. The ADHs are immunologically related as determined by Ouchterlony double diffusion experiments. These results suggest that the isozymes are encoded by different structural gene loci derived from a common ancestral gene.Financial support was provided by the National Cancer Institute of Canada and the Medical Research Council of Canada, Grant MT4860. J.-P. Thirion is a Research Scholar of the Science Research Council of Quebec.     

The effect of variable mechanical impedance on the control of antagonistic muscles

Most models of muscle have assumed that the series elastic element has a constant stiffness, although experimentally this is not true, either at the level of individual cross-bridges or that of the whole muscle. In this paper elastic and viscous elements are introduced whose properties vary systematically with activity levels as has been found experimentally. The effects of these nonlinear variations on the methods for optimally controlling a pair of antagonistic muscles are calculated. Although the nonlinearities add some complexity to the derivation and are important to the mechanism of force generation in the muscle, they do not qualitatively change the overall control of movement.This work was partly supported by the Natural Sciences and Engineering Research Council of Canada NSERC OGP-4345 and by the Medical Research Council of Canada Grant PG-47 through the University of Alberta     

Ultrastructural localization of acid phosphatase in the posterior pituitary of the dehydrated rat

Summary Acid phosphatase (AcPase) was localized by means of electron-microscopic histochemistry and estimated biochemically in the posterior pituitary of rats deprived of water, given 2% NaCl ad libitum, or given tap water ad libitum over 6 days. Autophagic vacuoles, some of which gave a positive AcPase reaction, often contained neurosecretory granules (NSG) in nerve endings of control animals on tap water. Nerve endings of water-deprived or salt-treated rats were depleted of NSG, but frequently contained dense membranous residual bodies, some of which appeared to enclose microvesicles. Smooth endoplasmic reticulum located in axons and terminals appears to be a source of hydrolytic enzymes for neurohypophysial lysosomes. The total amount of AcPase per posterior lobe increased progressively to 40% above control levels after 6 days of water deprivation or salt administration, and this increase may reflect accelerated production of neuronal components in neurohypophysial cells whose secretory rate has been stimulated by elevated body osmolarity.Supported by the Medical Research Council of Canada.Medical Research Associate of the Medical Research Council of Canada.     

The endocrine cells of the upper gut mucosa in dogs with transplantation of the pyloric antrum to the colon

Summary A previous examination, done by others, of the endocrine cells of the canine pyloric antrum following its transplantation to the colon evidenced an increase in their number; the cell types involved, however, were not individualized. The present study further characterizes the changes occurring in the endocrine cells of the pyloric antrum of dogs following transplantation to the colon. The main change observed consists of hyperplasia of the enterochromaffin cells, with minor qualitative modifications in the antral gastrin-producing cells being noted only by electron microscopy. The response of the enterochromaffin cells cannot be readily explained but might be related to similar enterochromaffin cell hyperplasias found in human stomachs with peptic ulcers. Antrum transplantation to the colon in dogs appears to provide a promising experimental model for the study of the relationship between gastrin and other humoral factors (probably biogenic amines) in the mechanism of gastric secretion under normal as well as abnormal circumstances.Supported by a grant from the Medical Research Council of Canada. While performing this research, Dr. J. Lechago was a recipient of a fellowship from the Medical Research Council of Canada.     

Fluorescence coupling across lipid bilayer membranes

Summary An energy transfer between donor and acceptor fluorophores across single lipid bilayer membranes is demonstrated. Anilino-naphthalene sulfonate is used as the donor chromophore: its fluorescence is enhanced by the presence of lipid and thus indicates association with the purely lipid membranes of our preparation of vesicles in suspension. Light emit ted by the donor molecules excites fluorescence of acriflavine, a suitable acceptor enclosed inside the vesicles. Absorption and fluorescence spectra of this system, in its components and as a whole, are presented in evidence for an energy transfer.Supported by a grant from the Medical Research Council of Canada. The results of this work were presented, in part, at the 17th Annual Meeting of the Biophysical Society, February 27–March 2, 1973, Columbus, Ohio.Scholar of the Medical Research Council of Canada.     

Red-light-enhanced conversion of tritiated gibberellin A9 into other gibberellin-like substances in homogenates of etiolated barley leaves

Summary Irradiation of homogenates of etiolated barley leaves with red light resulted in an increase in the levels of gibberellin (GA)-like substances as compared to dark controls. When homogenates were fed with [³H]-GA₉ there was as incorporation of the radioactivity into a number of other GA's: this process occurred to a greater extent in red light than in darkness, and could be inhibited by boiling the extract prior to addition of the [³H]-GA₉.Supported by National Research Council (Canada) grant A-5727 (Dr. D. M. Reid).Supported by National Research Council (Canada) grant A-2585 (Dr. R. P. Pharis).Supported by NATO-Science Research Council (U. K.) Postdoctoral Fellowship.     

The lymphocyte plasma membrane: Locus of control in the immune response

Summary The lymphocyte plasma membrane is the locus of events which control the immune response. T and B lymphocytes, which mediate cellular and humoral immunity respectively, show distinctive plasma membrane morphologies and cell surface receptors. The dynamic state of these plasma membrane components is emphasized by their lateral mobility in the fluid plane of the membrane, as well as variation in their structure or expression as the lymphocyte proliferates and differentiates in response to stimulation by antigen or mitogens. The best understood membrane glycoproteins are surface membrane immunoglobulins that serve as antigen receptors on B cells, and the histocompatability-β ₂ microglobulin complex that has an immunoglobulin-like structure. Other less well defined surface structures showing modulation during the cell cycle may affect growth regulation of proliferating lymphocytes. Some of these are shared by fetal and neoplastic cells. Major theories of lymphocyte signaling are discussed, and the early events in lymphocyte activation are reviewed. While a complete model encompassing all these early events is not yet possible, the central issues can be usefully discussed in terms of receptor-transducer-effector concepts derived by strong parallels from a knowledge of hormone-membrane interactions. Presented in the formal symposium on Information Transfer in Eukaryotic Cells, at the 26th Annual Meeting of the Tissue Culture Association, Montreal, Quebec, June 2–5, 1975. Supported by: Medical Research Council of Canada and National Cancer Institute of Canada. Scholar of the Medical Research Council of Canada.     

The glomus cell of the carotid labyrinth of Xenopus laevis

Summary In antral mucosa of the mouse stomach, the volume of mucus in mucous cells was measured morphometrically to determine whether this value changes during cell migration from the base of the pit to the surface. Both the volume density of mucous granules (the fraction of cell volume occupied by the granules) and the volume of intracellular mucus were reduced to about half in surface cells compared with those of upper pit cells. This indicates that mucus secretion is substantial during the later part of the lifespan of these cells, and is not due simply to the shedding of senescent cells.Supported by a grant from the National Health and Medical Research Council     

Acetylcholine and cholinesterases (assays and light- and electron microscopical histochemistry) in different parts of the pituitary of rat,rabbit and domestic pig

Summary Acetylcholine was measured by bioassay and cholinesterases by colorimetric assay and by light and electron microscopical histochemistry in the pars nervosa, pars intermedia and pars distalis of the rat, rabbit and domestic pig pituitaries. The highest ACh concentration was found in the rat pituitary. More butyrylcholinesterases and less acetylcholinesterase was found in the rat pituitary than in the rabbit and pig pituitaries. Light microscopical histochemistry showed greater depositions of reaction products in the rat pituitary than in the other two species. This was predominantly due to butyrylcholinesterases in the pars nervosa-pars intermedia junctional region of the rat pituitary. Electron microscopical histochemistry was of limited value for quantitative estimates of distribution and localization of cholinesterases. However, the ultrastructural localization showed that most of the reaction product in the pars nervosa was associated with pituicytes with little or no reaction product in the neurosecretory terminals or in other nerve terminals. In the pars intermedia, the reaction products were primarily on the membranes of the nuclei and endoplasmic reticulum, and in some nerve terminals. No conclusions concerning the role of acetylcholine and cholinesterase in the release of the neurosecretory hormones could be made on the basis of these findings.Supported by Medical Research Council of Canada.University of Calgary Postdoctoral Fellow. Present address: Department of Pharmacology, St. Thomas's Hospital Medical School, London S.W.1., England.MRC (Canada) Postdoctoral Fellow.Associate, Medical Research Council of Canada.Research Associate of the Consejo Nacional de Investigaciones Cientificas y Tecnicas, Argentina. Present address. Anatomisches Institut der Universität, D-6300 Gießen, Friedrichstraße 24 (Federal Republic of Germany)     

Electron microscopic localization of monoamine oxidase in the rat liver

Summary Two methods have been employed to localize monoamine oxidase activity in the cells of rat liver, using either 2-(2′-benzothiazolyl)-5-stryl-3-(4′-phtalhydrazidyl) tetrazolium chloride (BSPT) or ferricyanide as electron acceptor. With both methods monoamine oxidase activity was found both in the inner and the outer mitochondral membrane, although the outer membrane appeared the most probable location. In addition the BSPT method but not the ferricyanide method, revealed monoamine oxidase activity in the endoplasmatic reticulum. The results obtained by the two methods have been compared and are discussed in view of available biochemical data on monoamine oxidase. Supported by research grants from the National Research Council of Canada (A 3651), The Swedish Medical Research Council (4145) and M. Bergwall's Foundation, Stockholm.     

Detection of feedback in the central nervous system using system identification techniques

An analysis method to detect the presence of feedback between biological signals, particularly those associated with the central nervous system, is presented. The technique is based on recent results in the system identification literature involving the concept of a feedback free process. It may be applied to volume conducted signals such as EEG and EMG, as well as to neuronal spike trains through the use of a data transformation procedure. The utility of the technique is then demonstrated in a study of the relationship between Parkinsonian tremor and certain tremor cells found in the thalamus of Parkinsonian patients, using data collected during thalamotomies. The results obtained suggest that feedback mechanisms may be an important factor contributing to Parkinsonian tremor.This research was supported by the Natural Sciences and Engineering Research Council of Canada, The Medical Research Council of Canada, and Bell-Northern Research     

Application of optimal multichannel filtering to simulated nerve signals

The optimal linear filters derived in the preceding paper can be thoroughly evaluated using computer simulations, based on the properties of mammalian sensory and motor nerve fibres. Using reasonable values for action potential waveforms, conduction velocity and electrode noise, good separation of motor and sensory signals can be obtained. The performance of the filters is degraded by 1) increasing the electrode noise, 2) introducing dispersion in the conduction velocities, or 3) variation in the waveform of the action potentials from that used in designing the filters. However, the variations needed to seriously degrade performance are quite large compared to those which are likely to be present in mammalian nerves. Use of these filters to distinguish different classes of sensory (or motor) signals based on conduction velocity is discussed.This work was partially supported by the Technical Research Council of Denmark (Grant 516-6703.E406), the Medical Research Council of Canada (Grant MRC-MT3307) and the National Research Council of Canada (Grant NRC A-4345)     

Duplication of a peripheral sensory neuron in the cockroach Periplaneta americana

Summary We have recently examined the electrophysiology and ultrastructure of approximately 100 tactile spines from the metathoracic legs of adult cockroaches. In only one animal the single sensory neuron that innervates the spine was replaced with a pair of apparently identical neurons which we believe were both functional. As far as we are aware this is the first reported study of unprovoked duplication in a peripherally-located insect sensory neuron.Supported by the Canadian Medical Research Council and the Alberta Heritage Foundation for Medical Research     

Smooth endoplasmic reticulum proliferation in mouse enterocytes induced by fructose feeding

Summary Adult male mice receiving a fructose diet show, after three days, a large proliferation of the smooth endoplasmic reticulum in the jejunal absorptive cells. This extension is a secondary stage of the trememdous increase of the glucose-6-phosphatase activity and seems to result from a crypt regulation. Glucose feeding does not provoke the same morphologic changes. This work was supported by a research grant from the Medical Research Council of Canada. Dr. D. Maestracci Ph. D. is a recipient of a Centennial Fellowship of the Medical Research Council of Canada. Mr. D. Ménard is a recipient of a studentship of the Medical Reserach Council of Canada. The authors are greatly indebted to Mrs. S. Sinave for her skillful technical assistance.     

The influence of contact guidance on the orientation of colonies of subcultured vascular smooth muscle cells

Summary Subcultures of smooth muscle cells derived from rat thoracic aorta were grown on plane plastic substrata and on plastic substrata having ridges molded in them by a heated, ruled template. The cells were found to have a very high degree of contact guidance when distributed sparsely on the ridged substrata. When the cell density increased multilayered, elongated colonies formed. On plane substrata these were irregular, curved, and disposed in all directions. On the ridged substrata, however, the colonies were straight, evenly spaced, and positioned at right angles to the ridges. Supported by Grant MT1011 from the Medical Research Council of Canada.     

Surface morphology of lens fibers from eyes of normal and microphthalmic (Browman) rats

Summary The surface features of cortical fibers from lenses of normal adult rats and microphthalmic rats of the Browman strain have been studied by scanning electron microscopy. In the normal lenses, superficial cortical fibers follow a straight course from inner to outer pole whereas the deeper cortical fibers, while straight near the poles, pursue an undulating or zig-zag course at and near the equator. Almost all of the fibers are hexagonal in cross section and all fibers throughout their entire length are bound by interdigitating processes at each corner of the hexagon to corners of two adjacent fibers. Some fibers are also affixed by a single row of ball and socket junctions located on their broad outer and inner surfaces. Lens fibers from Browman rats display both minor and major abnormalities. These included segmentation, formation of incisures and lateral protrusions, corrugation and villous-like alteration of the broad fiber surface and development of parallel ridges on broad surfaces in a basket-weave pattern.Supported by The Medical Research Council of CanadaResearch Fellow of The Medical Research Council of Canada     

Bf polymorphism. A very fast variant from Nigeria

Summary In a collection of Nigerian serum samples typed for alleles of factor B of the alternative complement pathway, a very high frequency of Bf^F was found (0.69). In addition, a new variant was found in two samples. This variant (F^1.29) moved faster than BfF₁. It was hemolytically active.Supported in part by The Medical Research Council of Canada     

Analytical review: The pathogenesis of diabetes mellitus and its relationship to biological aging

Summary Recent studies on the pathogenesis of diabetes mellitus have been reviewed. The tendency to develop the disease is inherited, but other factors influence its expression, particularly aging. The hypothesis is advanced that diabetes is a heterogeneous disorder along a continuum of severity; its basis is a thrifty genotype that promotes survival both under conditions of privation, and in early stages of the lifespan, at the expense of accelerated aging later in the lifespan and/or under conditions of excess.Supported by grants from the Medical Research Council of Canada and the Canadian Diabetic Association Foundation Fund, during the tenure of a scholarship from the Medical Research Council.